Field of the Invention
This disclosure relates to a fluoride fluorescent material, a method for producing the same, and a light emitting device.
Description of the Related Art
A light emitting diode (LED) is a semiconductor light-emitting element produced from a metal compound, such as gallium nitride (GaN). Various types of light emitting devices that emit light of, e.g., white color, bulb color, or orange color have been developed using such a semiconductor light-emitting element in combination with a fluorescent material. Such light emitting devices are able to emit, e.g., white light by the light color mixture principle. Well known systems that emit white light include systems using a light emitting element that emits ultraviolet light and three types of fluorescent materials that emit red (R), green (G), and blue (B) light, and systems using a light emitting element that emits blue light and a fluorescent material that emits, e.g., yellow light. Light emitting devices that employ systems using a light emitting element that emits blue light and a fluorescent material that emits, e.g., yellow light are demanded in a wide variety of fields, including lighting, such as fluorescent lamps, car lights, displays, and backlights for liquid crystals.
Conventional red-light emitting fluorescent materials that have an excitation band in the blue region and exhibit an emission peak with a narrow half bandwidth include fluoride fluorescent materials having a composition, such as K2AlF5:Mn4+, K3AlF6:Mn4+, K3GaF6:Mn4+, Zn2AlF7:Mn4+, KIn2F7:Mn4+, K2SiF6:Mn4+, K2TiF6:Mn4+, K3ZrF7:Mn4+, Ba0.65Zr0.35F2.70:Mn4+, BaTiF6:Mn4+, K2SnF6:Mn4+, Na2TiF6:Mn4+, Na2ZrF6:Mn4+, or KRbTiF6:Mn4+. Various improvements to their production methods have been studied (see, e.g., Japanese Laid-open Patent Publication No. 2012-224536).
In connection with the above, a method for producing an Mn4+-activated red light-emitting fluoride fluorescent material that has a small specific surface area and is said to have superior light emitting properties is disclosed (see, e.g., Japanese Laid-open Patent Publication No. 2010-209331).